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 Title: Ionization Energies Of Para-h2 From Zero-quantum-defect Positions Author(s): Hölsch, Nicolas Contributor(s): Merkt, Frédéric Subject(s): Mini-symposium: Precision Spectroscopy for Fundamental Physics Abstract: From the precise measurement of the ionization energy of H$_2$ its dissociation energy can be determined\footnote{N. H\"olsch, M. Beyer, E.J. Salumbides, K.S.E. Eikema, W. Ubachs, Ch. Jungen, and F. Merkt, Phys. Rev. Lett., 122(10), 103003 (2019)}, which serves as a benchmark quantity for QED calculations\footnote{M. Puchalski, J. Komasa, P. Czachorowski, and K. Pachucki, Phys. Rev. Lett., 122(10), 103003 (2019)}. Additionally, measurements of ionization energies corresponding to higher rovibrational levels of the ion enable the determination of rovibrational intervals in H$_2^+$\footnote{C. Haase, M. Beyer, Ch. Jungen, and F. Merkt, J. Chem. Phys. 142(6), 064310 (2015)}. These intervals can be calculated extremely precisely for one-electron systems, offering the prospect of improving the value of fundamental constants\footnote{I.V. Kortunov, S. Alighanbari, M.G. Hansen, G.S. Giri, V.I. Korbov, and S. Schiller, Nat. Phys., 1-5 (2021)}. Until now, the most precise determinations of the ionization energies of molecular hydrogen have relied on the extrapolation of Rydberg series using multichannel quantum-defect theory (MQDT) and quantum defects extracted from high-precision measurements of Rydberg-Rydberg transitions using millimeter-wave (mmW) spectroscopy\footnote{D. Sprecher, Ch. Jungen, and F. Merkt, J. Chem. Phys. 140, 104303:1-18 (2014)}. The uncertainty of these extrapolations are typically larger than 500~kHz, currently representing the dominant source of uncertainty in the determinations of ionization energies. Additionally, autoionization lifetimes impede mmW measurements above the lowest ionization threshold which renders accurate extrapolations to higher rovibrational levels of the ion difficult. We present here a method to determine the binding energies of Rydberg states without having to resort to an extrapolation using MQDT. We carry out precision measurements of the linear Stark manifolds associated with near-degenerate high-$l$ states by mmW spectroscopy in the presence of intentionally applied electric fields. Extrapolating the linear Stark manifold to zero field yields accurate values of the zero-quantum-defect positions, given by $-\mathcal{R}_{\mathrm{H}_2}/n^2$ relative to the ionization thresholds. This method will be illustrated for Rydberg states of H$_2$ above $n=50$, circumventing the current bottlenecks and opening the route for order-of-magnitude improved ionization energies. Issue Date: 2021-06-23 Publisher: International Symposium on Molecular Spectroscopy Genre: Conference Paper / Presentation Type: Text Language: English URI: http://hdl.handle.net/2142/111302 Date Available in IDEALS: 2021-09-24
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